Stock-Based Compensation (Details 4) (USD $) In Thousands, except Per Share data, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2013	Dec. 31, 2012
Number of Shares
Outstanding at the beginning of the period (in shares)	18,066
Granted (in shares)	3,212
Exercised (in shares)	(665)
Forfeited (in shares)	(258)
Outstanding at the end of the period (in shares)	20,335	18,066
Number of stock option exercisable	15,243
Number of shares vested and expected to vest	20,007
Weighted Average Exercise Price
Outstanding at the beginning of the period (in dollars per share)	$ 3.50
Granted (in dollars per share)	$ 6.12
Exercised (in dollars per share)	$ 2.34
Forfeited (in dollars per share)	$ 6.08
Outstanding at the end of the period (in dollars per share)	$ 3.91	$ 3.50
Weighted average exercise price for exercisable option (in dollars per share)	$ 3.02
Weighted average exercise price of shares vested and expected to vest (in dollars per share)	$ 3.87
Weighted Average Remaining Contractual Term
Outstanding at the beginning of the period	6 years 4 months 10 days	6 years 6 months 14 days
Outstanding at the end of the period	6 years 4 months 10 days	6 years 6 months 14 days
Exercisable	5 years 5 months 12 days
Vested and expected to vest	6 years 3 months 22 days
Aggregate Intrinsic Value
Outstanding at the beginning of the period (in dollars)	$ 51,486
Outstanding at the end of the period (in dollars)	20,411	51,486
Options exercisable (in dollars)	20,336
Shares vested and expected to vest (in dollars)	$ 20,406